<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            padding: 0;
            margin: 0;
        }
        .a{
            width: 200px;
            height: 200px;
            background-color: #bfa;
            position: relative;
            margin-left: 10px;
            padding-left: 10px;
            border-left: 100px solid red;
            /* border-left: 100px solid transparent; */
        }
        .b{
            width: 50px;
            height: 50px;
            background-color: yellow;
            position: absolute;

        }
        .sticky{
            width: 300px;
            height: 300px;
            background-color: red;
            margin-top: 20px;
            position: sticky;
            top: 0;
            box-shadow: 0 0 10px silver;
        }
    </style>
</head>
<body>
    <div class="a">
        <div class="b"></div>
    </div>
    <div class="sticky">1</div>
    <div class="sticky">2</div>
    <div class="sticky">3</div>
    <div class="sticky">4</div>
</body>
</html>